Wall crawling robots

ABSTRACT

Described herein is electroadhesion technology that permits controllable adherence between two objects. Electroadhesion uses electrostatic forces of attraction produced by an electrostatic adhesion voltage, which is applied using electrodes in an electroadhesive device. The electrostatic adhesion voltage produces an electric field and electrostatic adherence forces. When the electroadhesive device and electrodes are positioned near a surface of an object such as a vertical wall, the electrostatic adherence forces hold the electroadhesive device in position relative to the surface and object. This can be used to increase traction or maintain the position of the electroadhesive device relative to a surface. Electric control of the electrostatic adhesion voltage permits the adhesion to be controllably and readily turned on and off.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from co-pending and commonly owned U.S.patent application Ser. No. 11/757,913 filed Jun. 4, 2007, whichapplication in turn claims priority under 35 U.S.C. §119(e) from a) U.S.Provisional Patent Application No. 60/803,953 filed Jun. 5, 2006, namingHarsha Prahlad et al. as inventors, and titled “Wall-Climbing Robot forThree-Dimensional Mobility in Urban Environments,” and b) U.S.Provisional Patent Application No. 60/866,555 filed Nov. 20, 2006,naming Harsha Prahlad et al. as inventors, and titled “Wall-ClimbingRobot for Three-Dimensional Mobility in Urban Environments,” with all ofthese applications being incorporated by reference herein in theirentirety for all purposes.

U.S. GOVERNMENT RIGHTS

This application was made in part with government support under contractnumber N66001-05-C-8019 awarded by the Department of Defense. Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

The present invention relates generally to devices and methods thatprovide electrically controllable adhesion. More particularly, thepresent invention relates to the use of electrical energy andelectrostatic forces to provide adhesive forces between two objects.

BACKGROUND OF THE INVENTION

Controlled adhesion remains an unmet technological need. For example,for over twenty years the robotics field has tried to invent a reliableform of controlled adhesion on a wide range of substrates for wallcrawling robots, without success. Success in controlled adhesion can bedefined by a technology that is: controllable, reliable, and robustenough to work on a sufficient range of everyday wall and naturalmaterials, and those encountered under real environmental conditions,such as wet or dusty surfaces, highly sloped surfaces, or slipperysurfaces.

The existing technologies, many of which are still in the lab and not incommercial production, marked for wall crawling fail to provide the fullrange of these capabilities. Chemical adhesives are always “on.” Whilethey require no energy to perch, robots that employ chemical adhesiveclamping technologies require a lot of energy to climb and traversehorizontally (requiring more batteries and weight), fighting theadhesion which cannot be switched off. Chemical adhesive technologiescan also attract dust and other debris that quickly reduce theireffectiveness. Suction (active or passive) works effectively only onsmooth surfaces. Also, conventional suction cups suffer from leaks andcannot manage dusty surfaces. Mechanical claws only work on very roughor penetrable surfaces and often leave damaging marks. Syntheticgecko-like skin can become easily damaged or befouled after repeated use(as few as five cycles), and does not work on wet surfaces.

Controlled adhesion is also useful outside of robotics. Robust devicesand methods to provide adhesion would be beneficial.

SUMMARY

The present invention provides electroadhesion technology that permitscontrollable adherence between two objects. Electroadhesion useselectrostatic forces of attraction produced by an electrostatic adhesionvoltage, which is applied using electrodes in an electroadhesive device.The electrostatic adhesion voltage produces an electric field andelectrostatic adherence forces. When the electroadhesive device andelectrodes are positioned near a surface of an object such as a verticalwall, the electrostatic adherence forces hold the electroadhesive devicein position relative to the surface and object. This can be used toincrease traction or maintain the position of the electroadhesive devicerelative to a surface. Electric control of the electrostatic adhesionvoltage permits the adhesion to be controllably and readily turned onand off. Devices described herein, such as mobile devices and robots,use this controlled electroadhesion to navigate vertical walls and othernon-flat surfaces.

In one aspect, the present invention relates to a mobile device. Themobile device includes a body and at least one electroadhesive devicemechanically coupled to the body. The at least one electroadhesivedevice is configured to detachably adhere to the substrate, andincludes: a deformable surface for interfacing with a surface of asubstrate, a first electrode configured to apply a first voltage at afirst location of the deformable surface, and a second electrodeconfigured to apply a second voltage at a second location of thedeformable surface. The difference in voltage between the first voltageand second voltage includes an electrostatic adhesion voltage thatproduces an electrostatic force between the at least one electroadhesivedevice and the substrate that is suitable to maintain a current positionof the at least one electroadhesive device relative to the substrate.The insulation material disposed between the first electrode and thesecond electrode and configured to substantially maintain theelectrostatic adhesion voltage difference between the first electrodeand the second electrode.

In another aspect, the present invention relates to an electroadhesivedevice configured to adhere two objects together. The electroadhesivedevice includes a body with a first surface and a second surface. Theelectroadhesive device also includes a first electrode configured toapply a first voltage at a first location of the first surface, and asecond electrode configured to apply a second voltage at a secondlocation of the first surface. The difference in voltage between thefirst voltage and second voltage includes an electrostatic adhesionvoltage that produces a first electrostatic force between theelectroadhesive device and a first object that is suitable to adhere asurface of the first object to the first surface. The difference involtage between the first voltage and second voltage includes anelectrostatic adhesion voltage that produces a second electrostaticforce between the electroadhesive device and a second object that issuitable to adhere a surface of the second object to the second surface.

In yet another aspect, the present invention relates to a method ofascending a wall. The method includes positioning an electroadhesiondevice in proximity to a surface of the wall. The method also includesapplying an electrostatic adhesion voltage difference between a firstelectrode at a first location of the electroadhesion device and a secondelectrode at a second location of the electroadhesion device. The methodfurther includes adhering the electroadhesion device to the wall surfaceusing an electrostatic attraction force provided by the electrostaticadhesion voltage difference. The method additionally includes ascendingthe wall while the electroadhesion device adheres to the wall.

These and other features and advantages of the present invention will bedescribed in the following description of the invention and associatedfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simplified electroadhesive device in accordance with oneembodiment of the present invention.

FIG. 2 shows the electroadhesive device of FIG. 1 attached to a surfaceof a vertical wall.

FIG. 3 shows an electric field formed in the substrate of a structure asresult of the voltage difference between electrodes in theelectroadhesive device of FIG. 1.

FIG. 4A shows an electroadhesive device with a set of electrodesembedded in an insulating material in accordance with another embodimentof the present invention.

FIG. 4B shows provision of a suitable electrostatic adhesion voltage toelectrodes of the electroadhesive device of FIG. 4A and the electricfields that result.

FIG. 4C shows an electroadhesive device with a set of electrodesdisposed on an inside surface of an insulating layer in accordance withanother embodiment of the present invention.

FIG. 4D shows provision of a suitable electrostatic adhesion voltage toelectrodes of the electroadhesive device of FIG. 4C and the resultantelectric fields.

FIG. 4E shows an electroadhesive device with a first set of electrodesdisposed on an inside surface of insulating layer, and a second set ofelectrodes disposed on the opposite surface of the insulating layer, inaccordance with another embodiment of the present invention.

FIG. 4F shows electric fields for the electroadhesive device of FIG. 4E.

FIG. 4G shows an electroadhesive device in accordance with anotherembodiment of the present invention.

FIG. 4H shows the resultant electric fields for electroadhesive device.

FIG. 4I shows an electroadhesive device in accordance with anotherembodiment of the present invention.

FIG. 4J shows one suitable example of phase shifted input for the threevoltage pattern of FIG. 4I in accordance with a specific embodiment ofthe present invention.

FIG. 5A shows a deformable electroadhesive device conforming to theshape of a rough surface in accordance with a specific embodiment of thepresent invention.

FIG. 5B shows a surface of a deformable electroadhesive device initiallywhen the device is brought into contact with a surface of a structure inaccordance with a specific embodiment of the present invention.

FIG. 5C shows the surface shape of electroadhesive device of FIG. 5B andwall surface after some deformation in the electroadhesive device due tothe initial force of electrostatic attraction and compliance.

FIG. 6A shows an electroadhesive device with patterned electrodes inaccordance with another embodiment of the present invention.

FIG. 6B shows an electroadhesive device with patterned electrodes inaccordance with another embodiment of the present invention.

FIG. 6C shows a variation of the device of FIG. 6A device usingconducting cilia in accordance with another specific embodiment of thepresent invention.

FIGS. 7A-7C illustrate the concept of peeling for an electroadhesivedevice.

FIGS. 7D and 7E show partial detachment of an electroadhesive device.

FIGS. 7F and 7G show an electroadhesive device that includes a gridstructure to subdivide the overall electroadhesive device area inaccordance with another embodiment of the present invention.

FIGS. 7H and 7I show a peel-resistant electroadhesive device inaccordance with another embodiment of the present invention.

FIG. 8 shows control and conditioning circuitry suitable for providing asuitable electrostatic adhesion voltage to electrodes of anelectroadhesive device in accordance with one embodiment of the presentinvention.

FIG. 9 shows a method of adhering objects using electroadhesion inaccordance with one embodiment of the present invention.

FIGS. 10A-10B shows a tracked wall-crawling robot modified withelectroadhesive devices in accordance with a specific embodiment of thepresent invention.

FIG. 10C shows the wall-crawling robot of FIG. 10B moving from ahorizontal surface to a vertical wall and to another horizontal surface.

FIG. 11A illustrates a wall-crawling robot that uses electroadhesion inaccordance with another specific embodiment of the present invention.

FIG. 11B shows a perspective view of the tire for the robot of FIG. 11Ain closer detail.

FIG. 12 shows a robot in accordance with another specific embodiment ofthe present invention.

FIG. 13 shows a robot in accordance with another embodiment of thepresent invention.

FIG. 14 shows electroadhesive handwear and electroadhesive leg-pads inaccordance with a specific application embodiment.

FIGS. 15A and 15B show electroadhesive scaling devices in accordancewith two specific application embodiments.

FIGS. 16A-16C show a detachable double-sided electroadhesive device inaccordance with another specific embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described in detail with reference to a fewpreferred embodiments as illustrated in the accompanying drawings. Inthe following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art, that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process steps and/or structureshave not been described in detail in order to not unnecessarily obscurethe present invention.

Electrically Controlled Adhesion

As the term is used herein, ‘electroadhesion’ refers to the mechanicalcoupling of two objects using electrostatic forces. Electroadhesion asdescribed herein uses electrical control of these electrostatic forcesto permit temporary and detachable attachment between two objects. Thiselectrostatic adhesion holds two surfaces of these objects together orincreases the traction or friction between two surfaces due toelectrostatic forces created by an applied electric field. In oneembodiment, electrostatic adhesion of one material to another uses anelectric field across an insulating and deformable material.

Conventionally, electrostatic clamping was limited to holding two flat,smooth conductive surfaces together. The inventors have developedelectroadhesion devices and techniques that do not limit the materialproperties or surface roughness of the substrate being adhered to.

FIG. 1 shows a simplified electroadhesive device 10 in accordance withone embodiment of the present invention. FIG. 2 shows an electroadhesivedevice 10 attached to a surface 12. Surface 12 is part of a largerstructure 14 that includes material, or substrate, 16, which in thisinstance resembles a vertical wall. While the present invention willprimarily be described as devices and structures, those skilled in theart will also appreciate that the present invention relates to methodsof adhering objects using electroadhesion.

An electrostatic adhesion voltage is applied via electrodes 18 usingexternal control electronics (see FIG. 8) in electrical communicationwith the electrodes 18. As shown in FIG. 2, the electrostatic adhesionvoltage uses alternating positive and negative charges on adjacentelectrodes 18. As result of the voltage difference between electrodes18, and as shown in FIG. 3, a electric field 22 forms in the substrate16 of structure 14. The electric field 22 locally polarizes a dielectricmaterial 16 and thus causes electrostatic adhesion between theelectrodes 18 (and device 10) and the induced charges on the substrate16. The induced charges may be the result of the dielectric polarizationor from weakly conductive materials and leakage currents. While notwishing to be bound by theory, the induced electrostatic forces may alsouse the Johnson-Rahbeck effect to provide increased forces at lowerpower levels.

Thus, the electrostatic adhesion voltage provides an electrostaticforce, between the electroadhesive device 10 and material 16 beneathsurface 12, that maintains the current position of device 10 relative tothe surface. Suitable electrostatic adhesion voltages will be describedin further detail below. For a wall or other relatively verticalsurface, the electrostatic force between the electroadhesive device 10and surface 12 overcomes gravitational pull on the device 10, and holdsdevice 10 aloft. Device 10 may also be attached to other structures andhold these additional structures aloft, or it may be used on sloped orslippery surfaces to increase normal friction forces.

Removal of the electrostatic adhesion voltages from electrodes 18 ceasesthe electrostatic adhesion force between device 10 and surface 12. Thus,when there is no electrostatic adhesion voltage between electrodes 18,electroadhesive device 10 can move freely relative to surface 12. Thiscondition allows electroadhesive device 10 to move before and after anelectrostatic adhesion voltage is applied. Robots and other devices thatleverage this control for wall-crawling will be described in furtherdetail below. In addition, as will be expanded upon below, electricalactivation and de-activation enables fast adhesion and detachment, suchas response times less than about 50 milliseconds, while consuming smallamounts of power.

Electro adhesive device 10 of FIG. 1 includes electrodes 18 on theoutside surface of insulating material 20 (e.g., they are exposed on theoutside surface of insulating material 20 and may contact wall surface12). This embodiment is well suited for controlled attachment toinsulating and weakly conductive materials and substrates 16. Otherelectroadhesive device 10 relationships between electrodes 18 andinsulating material 20 are contemplated and suitable for use with abroader range of materials including conductive materials.

FIG. 4A shows an electroadhesive device 10 b with a set of electrodes 18embedded in the insulating material 20 in accordance with anotherembodiment of the present invention. FIG. 4B shows provision of asuitable electrostatic adhesion voltage to electrodes 18 ofelectroadhesive device 10 b and the electric fields 22 from charges onelectrodes 18 that result when adhering to a substrate 16.

FIG. 4C shows an electroadhesive device 10 c with a set of electrodes 18disposed on an inside surface 23 of insulating layer 20, opposite to asurface 25 of insulating layer 20 that is meant to contact and adhere toa wall, in accordance with another embodiment of the present invention.FIG. 4D shows provision of a suitable electrostatic adhesion voltage toelectrodes 18 of electroadhesive device 10 c and the resultant electricfields 22 from charges on electrodes 18.

FIG. 4E shows an electroadhesive device 10 d with a first set 40 ofelectrodes 18 disposed on an inside surface 23 of insulating layer 20,and a second set 42 of electrodes disposed on the opposite surface 25 ofinsulating layer 20, in accordance with another embodiment of thepresent invention. FIG. 4F shows the resultant electric fields 22 fromcharges on electrodes 18 for electroadhesive device 10 d.

Expanding upon electroadhesive attraction, the exact mechanism for forcegeneration will depend on conductivity and dielectric constant ofmaterial 16 under surface 12. Notably, the present invention is notlimited by the electrical characteristics of the substrate being adheredto, even though electroadhesion is largely based on electricalprinciples. Indeed, electroadhesion as described herein works well forboth conductive and non-conductive (or insulating) substrates 16.

Returning back to FIGS. 2 and 3, when material 16 acts as an insulatorfor the voltage difference between the alternate positive and negativecharges applied by electrodes 18, electric fields 22 from charges onelectrodes 18 polarize a dielectric and insulating substrate and thuscause electrostatic adhesion between electroadhesive device 10 and theinduced polarization charges in material 16 of structure 14.

However, when material 16 is conductive, free charge flows withinsubstrate 16, and the charged electrodes 18 are attracted to theconductive material by electrostatic forces. The same mechanism alsoapplies to a damp and insulating substrate 16, where the moisture orother conductive particles lodged in the surface act as a conductivesurface on an otherwise insulating material. Of course, if substrate 16is too conductive the control electronics may not be able to maintain anadequate electroadhesion voltage and an insulated embodiment such asthat shown in FIG. 4A is used.

While the electroadhesive device 10 attaches well to both conductive andinsulating substrates 16, it may be helpful to distinguish between thetwo to help show the range of materials that device 10 can attach to. Aconductive material may be defined as a material with a resistivity lessthan about 10¹² ohm-cm. An insulating material may be defined as amaterial with a resistivity greater than about 10¹² ohm-cm. For thisdefinition, the conductive materials include true conductors such asmetals and also semiconductive materials and materials such as concrete,most woods and rock that would ordinarily be thought of as insulating.However, as will be described, the practical boundary between insulatingand conductive materials depends in part on the geometry and featuresizes of the electroadhesive device.

Notably, then, for the same electroadhesive devices discussed so far,the same electroadhesive device 10 geometry and operation (applyelectrostatic adhesion voltages to electrodes 18) can be used to clampto both insulating and conductive substrates. This represents onedistinguishing feature of electroadhesive device 10.

In some cases, the electroadhesive device is designed to use thesubstrate as an insulation material. FIG. 4G shows an electroadhesivedevice 10 g in accordance with another embodiment of the presentinvention. FIG. 4H shows the resultant electric fields 22 forelectroadhesive device 10 g.

Electroadhesive device 10 g includes two electrodes 18 that directlycontact substrate 16. Electrodes 18 attach to mechanically separate pads57. For example, each pad 57 may be included in a separate foot of arobot.

Notably, for electroadhesive device 10 g, there is no insulationmaterial 20 between the electrodes 18 included in the electroadhesivedevice. In this instance, substrate substrate 16 acts as an insulationmaterial between the electrodes. This design still permitselectroadhesive forces to be generated, but does not work on conductivesubstrates 16 (insulation material between one or both of the electrodes18 may then be used, such as shown in FIGS. 4A-4F).

Another distinguishing feature of electroadhesive devices describedherein is the option to use deformable surfaces and materials inelectroadhesive device 10 as shown in FIG. 5. In one embodiment, one ormore portions of electroadhesive device 10 are deformable. In a specificembodiment, this includes surface 30 on device 10. In anotherembodiment, insulating material 20 between electrodes 18 is deformable.Electroadhesive device 10 may achieve the ability to deform usingmaterial compliance (e.g., a soft material as insulating material 20) orstructural design (e.g., see cilia or hair-like structures shown in FIG.6C or tracks 352 in FIG. 10A). In a specific embodiment, insulatingmaterial 20 includes a bendable but not substantially elasticallyextendable material (for example, a thin layer of mylar). In anotherembodiment insulating material 20 is a soft polymer with modulus lessthan about 10 MPa and more specifically less than about 1 MPa.

Electrodes 18 may also be compliant. Compliance for insulating material20 and electrodes 18 may be used in any of the electroadhesive devicearrangements 10 described above. Compliance in electroadhesive device 10permits an adhering surface 30 of device 10 to conform to surface 12features of the object it attaches to. FIG. 5A shows a compliantelectroadhesive device 10 conforming to the shape of a rough surface 12in accordance with a specific embodiment of the present invention.

Adhering surface 30 is defined as the surface of an electroadhesivedevice that contacts the substrate surface 12 being adhered to. Theadhering surface 30 may or may not include electrodes. In oneembodiment, adhering surface 30 includes a thin and compliant protectivelayer that is added to protect electrodes that would otherwise beexposed. In another embodiment, adhering surface 30 includes a materialthat avoids retaining debris stuck thereto (e.g., when electrostaticforces have been removed). Alternatively, adhering surface 30 mayinclude a sticky or adhesive material to help adhesion to a wall surfaceor a high friction material to better prevent sliding for a given normalforce.

Compliance in electroadhesive device 10 often improves adherence. Whenboth electrodes 18 and insulating material 20 are able to deform, theadhering surface 30 may conform to the micro- and macro-contours of arough surface 12, both initially and dynamically after initial chargehas been applied. This dynamic compliance is described in further detailwith respect to FIG. 5B. This surface electroadhesive device 10compliance enables electrodes 18 get closer to surface 12, whichincreases the overall clamping force provided by device 10. In somecases, electrostatic forces may drop off with distance (betweenelectrodes and the wall surface) squared. The compliance inelectroadhesive device 10, however, permits device 10 to establish,dynamically improve and maintain intimate contact with surface 14,thereby increasing the applied holding force applied by the electrodes18. The added compliance can also provide greater mechanicalinterlocking on a micro scale between surfaces 12 and 30 to increase theeffective friction and inhibit sliding.

The compliance permits electroadhesive device 10 to conform to the wallsurface 12 both initially—and dynamically after electrical energy hasbeen applied. This dynamic method of improving electroadhesion is shownin FIGS. 5B-5C in accordance with another embodiment of the presentinvention.

FIG. 5B shows a surface 30 of electroadhesive device 10 initially whenthe device 10 is brought into contact with surface 12 of a structurewith material 16. Surface 12 may include roughness and non-uniformitieson a macro, or visible, level (for example, the roughness in concretecan easily be seen) and a microscopic level (most materials).

At some time when the two are in contact as shown in FIG. 5B,electroadhesive electrical energy is applied to electrodes 18. Thiscreates a force of attraction between electrodes 18 and wall surface 12.However, initially, as a practical matter for most rough surfaces, ascan be seen in FIG. 5B, numerous gaps 82 are present between devicesurface 30 and wall surface 12.

The number and size of gaps 82 affects electroadhesive clampingpressures. For example, at macro scales electrostatic clamping isinversely proportional to the square of the gap between the substrate 16and the charged electrodes 18. Also, a higher number of electrode sitesallows device surface 30 to conform to more local surface roughness andthus improve overall adhesion. At micro scales, though, the increase inclamping pressures when the gap is reduced is even more dramatic. Thisincrease is due to Paschen's law, which states that the breakdownstrength of air increases dramatically across small gaps. Higherbreakdown strengths and smaller gaps imply much higher electric fieldsand therefore much higher clamping pressures. The inventors havedetermined that clamping pressures may be increased, and electroadhesionimproved, by using a compliant surface 30 of electroadhesive device 10,or an electroadhesion mechanism that conforms to the surface roughness.

When the force of attraction overcomes the compliance in electroadhesivedevice 10, these compliant portions deform and portions of surface 30move closer to surface 12. This deformation increases the contact areabetween electroadhesive device 10 and wall surface 12, increaseselectroadhesion clamping pressures, and provides for strongerelectroadhesion between device 10 and wall 14. FIG. 5C shows the surfaceshape of electroadhesive device 10 and wall surface 12 after somedeformation in electroadhesive device 10 due to the initial force ofelectrostatic attraction and compliance. Many of the gaps 82 have becomesmaller.

This adaptive shaping may continue. As the device surface 30 and wallsurface 12 get closer, the reducing distance therebetween in manylocations further increases electroadhesion forces, which causes manyportions of electroadhesive device 10 to further deform, thus bringingeven more portions of device surface 30 even closer to wall surface 12.Again, this increases the contact area, increases clamping pressures,and provides for stronger electroadhesion between device 10 and wall 14.The electroadhesive device 10 reaches a steady state in conformity whencompliance in the device prevents further deformation and device surface30 stops deforming.

In another embodiment, electroadhesive device 10 includes porosity inone or more of electrodes 18, insulating material 20 and backing 24.Pockets of air may be trapped between surface 12 and surface 301; theseair pockets may reduce adaptive shaping. Tiny holes or porous materialsfor insulator 20, backing 24, and/or electrodes 18 allows trapped air toescape during dynamic deformation.

Thus, electroadhesive device 10 is well suited for use with roughsurfaces, or surfaces with macroscopic curvature or complex shape. Inone embodiment, surface 12 includes roughness greater than about 100microns. In a specific embodiment, surface 12 includes roughness greaterthan about 3 millimeters.

An optional backing structure 24, as shown in FIG. 1, 2, or 5A, attachesto insulating material 20, includes a rigid or non-extensible material,and provides structural support for the compliant electroadhesive device10 b. Backing layer 24 also permits external mechanical coupling toelectroadhesive device 10 b to permit the device to be used in largerdevices, such as wall-crawling robots and other devices and applicationsdescribed below.

With some electroadhesive devices 10, softer materials may warp anddeform too much under mechanical load, leading to suboptimal clamping.To mitigate these effects, electroadhesive device 10 may include agraded set of layers or materials, where one material has a lowstiffness or modulus for coupling to the wall surface and a secondmaterial, attached to a first passive layer, which has a thicker and/orstiffer material. Backing structure 24 may attach to the second materialstiffer material. In a specific embodiment, electroadhesive device 10included an acrylic elastomer of thickness approximately 50 microns asthe softer layer and a thicker acrylic elastomer of thickness 1000microns as the second support layer. Other thicknesses may be used.

The time it takes for the changes of FIGS. 5B and 5C may vary with theelectroadhesive device 10 materials, electroadhesive device 10 design,the applied control signal, and magnitude of electroadhesion forces. Thedynamic changes can be visually seen in some electroadhesive devices. Inone embodiment, the time it takes for device surface 80 to stopdeforming is between about 0.01 seconds and about 10 seconds. In othercases, the conformity ceasing time is between about 0.5 second and about2 seconds.

In some embodiments, electroadhesion as described herein permits fastclamping and unclamping times and may be considered almostinstantaneous. In one embodiment, clamping or unclamping may be achievedin less than about 50 milliseconds. In a specific embodiment, clampingor unclamping may be achieved in less than about 10 milliseconds. Thespeed may be increased by several means. If the electrodes areconfigured with a narrower line width and closer spacing then speed isincreased using conductive or weakly conductive substrates because thetime needed for charge to flow to establish the electroadhesive forcesis reduced (basically the “RC” time constant of the distributedresistance-capacitance circuit including both electroadhesive device andsubstrate is reduced). Using softer, lighter, more adaptable materialsin device 10 will also increase speed. It is also possible to use highervoltage to establish a given level of electroadhesive forces morequickly, and one can also increase speed by overdriving the voltagetemporarily to establish charge distributions and adaptations quickly.To increase unclamping speeds, a driving voltage that effectivelyreverses polarities of electrodes 18 at a constant rate may be employed.Such a voltage prevents charge from building up in substrate material 16and thus allows faster unclamping. Alternatively, a moderatelyconductive material 20 can be used between the electrodes 18 to providefaster discharge times at the expense of some additional driving powerrequired.

As the term is used herein, an electrostatic adhesion voltage refers toa voltage that produces a suitable electrostatic force to coupleelectroadhesive device 10 to a wall or substrate. The minimum voltageneeded for electroadhesive device 10 will vary with a number of factors,such as: the size of electroadhesive device 10, the materialconductivity and spacing of electrodes 18, the insulating material 20,the wall material 16, the presence of any disturbances toelectroadhesion such as dust, other particulates or moisture, the weightof any structures mechanically coupled to electroadhesive device 10,compliance of the electroadhesive device, the dielectric and resistivityproperties of the substrate, and the relevant gaps between electrodesand substrate. In one embodiment, the electrostatic adhesion voltageincludes a differential voltage between the electrodes 18 that isbetween about 500 volts and about 10 kilovolts. In a specificembodiment, the differential voltage is between about 2 kilovolts andabout 5 kilovolts. Voltage for one electrode can be zero. Alternatingpositive and negative charges may also be applied to adjacent electrodes18. Further description of electrical circuits and electricalperformance of electroadhesive device 10 is described in the nextsection of this patent application.

The resultant clamping forces will vary with the specifics of aparticular electroadhesive device 10, the material it adheres to, anyparticulate disturbances, wall surface roughness, etc. In general,electroadhesion as described herein provides a wide range of clampingpressures, generally defined as the attractive force applied by theelectroadhesive device divided by the area of the electroadhesive devicein contact with the wall. For purposes of illustration, clamping forcesfor electroadhesion can be simplified in terms of the normal clampingpressure (P_(N)), the friction coefficient (μ) between substrate andclamp, and the effective lateral adhesion pressure (P_(L)). Theeffective lateral adhesion pressure P_(L) represents the measuredmaximum lateral force without slippage divided by the area of surface30. The three quantities are related by:

P_(L)=μP_(N)  (Equation 1)

P_(L) is important for wall climbing applications, where gravity exertsa lateral force on the electroadhesive device 10, and it can beincreased either by increasing the normal clamping pressure P_(N), or byincreasing the friction coefficient. P_(N) is the important for mobilityon a ceiling where gravity exerts a normal force opposite to theelectroadhesive device 10.

The actual electroadhesion forces and pressure will vary with design anda number of factors. In one embodiment, electroadhesive device 10provides electroadhesive attraction pressures between about 0.7 kPa(about 0.1 psi) and about 70 kPa (about 10 psi). In a specificembodiment, electroadhesive device 10 provides pressures between about 2kPa (about 0.3 psi) and about 20 kPa (about 3 psi). The amount of forceneeded for an application may then be readily achieved by varying thecontacting and active surface 30 of electroadhesive device 10. Ingeneral, increasing the voltage increases electroadhesion forces. Also,decreasing the distance between the electrodes and surface increaseselectroadhesion forces. Further, increasing the active contact surface30 and electroadhesive device size increases electroadhesion forces. Forrobotic applications described below, the electroadhesive device sizesused for each robot will depend on a number of factors such as thenumber of pads used, robot weight, and robust factors (e.g., amultiplier of 1.5-10 for robust operation). For example, a clampingpressure of 0.125 psi can carry a 1 lb robot with two square pads ofdimensions 2 inches on each side, not including a safety factor forrobust operation.

One suitable solution to overcome less than ideal situations (e.g.,dust, difficult materials, rough surfaces, extremely wet surfaces, etc.)is simply to increase the electroadhesive device 10 area untilsufficient clamping force is achieved despite the wall disturbances.Since the electroadhesive devices 10 are light, increasing their area isunlikely to result in a significant increase in the overall weight of arobot for example.

For robots, increasing clamping pressures or electroadhesive devicesizes provides margins to accommodate less than ideal surfaces andsituations (e.g., rough surfaces, dust, etc.) and unpredictabledisturbances on the robot. It also decreases power requirements (byallowing lower voltage operation for the same clamping pressure), allowsgreater payloads, and permits faster and more robust locomotion. Inaddition, one can simply attach a large or additional electroadhesivedevices 10 to the other areas of a robot to enhance adhesive abilities.

So far, the present invention has been described in the context of asingle contact surface 30 attaching to a wall for electroadhesive device10. Multiple surfaces 30 are also suitable for use in a singleelectroadhesive device 10. When commonly attaching to a single wall, themultiple surfaces 30 may operate in concert for a single device 10, andthus reduce the forces and size for each individual surface 30. Forexample, a robot may include two or more electroadhesive surfaces 30coupled to a robotic actuator that is configured to position thesurfaces 30 on a wall surface.

The electrodes 18 may also be enhanced by various means, such aspatterned on an adhesive device surface to improve electroadhesiveperformance. FIG. 6A shows an electroadhesive device 10 e in accordancewith another embodiment of the present invention. Electroadhesive device10 e includes interdigitated top and bottom electrodes sets 40 and 42 onopposite sides of an insulating layer 44. In some cases, the electrodesas well as the insulating layer 44 may be compliant and composed ofelastomers to increase compliance. In one preferred embodiment themodulus of the elastomers is below about 10 MPa and in another preferredembodiment it is more specifically below about 1 MPa.

Electrode set 42 is disposed on a top surface 23 of insulating layer 44,and includes an array of linear patterned electrodes 18. A commonelectrode 71 electrically couples electrodes 18 in set 42 and permitselectrical communication with all the electrodes 18 in set 42 using asingle input lead to common electrode 71.

Electrode set 40 is disposed on a bottom surface 25 of insulating layer44, and includes a second array of linear patterned electrodes 18 thatis laterally displaced from electrodes 18 on the top surface. Set 40 mayalso include a common electrode (not shown).

The pitch, or planar spacing between individual electrodes 18 in sets 40and 42, may vary. The spacing in the cross section shown may becharacterized by electrode width 45 and pitch 47. Pitch 47 representsthe spacing between electrodes of different polarities, whether they areon the same or different side of the insulating layer 44. In a specificembodiment, electroadhesive device 10 e includes compliant carbonelectrodes with an about 1 millimeter electrode width 45 and an about 1millimeter pitch 47 between the electrodes. Other line widths andpitches are suitable for use. In another embodiment, pitch 47 is about 1centimeter. Generally speaking, narrower pitches 47 and widths 45 allowfaster clamping to more insulating or resistive substrates, while widerpitches 47 and widths 45 attract the electroadhesive device 10 to thesubstrate from a greater distance. In one embodiment, the pitch betweenthe electrodes can be non-uniform along the length of the clamp 10 toallow a variety of geometric electric fields to be setup. In anotherembodiment, the electrodes can be arranged in different two-dimensionalgeometry (eg. concentric rings).

Electrodes can be patterned on opposite sides of an insulating layer 44to increase the ability of the electroadhesive devices 10 e and 10 f towithstand higher voltage differences without being limited by breakdownin the airgap between the electrodes. Typically, when the electrodes 18are patterned on opposite sides of an insulator layer 44, the electrode18 spacing in each set 40 and 42 is much greater than the thickness ofthe elastomeric layer 44 (which has been exaggerated in the drawings forpurposes of illustration, along with exaggerating the thickness of theelectrodes, which may be only several micrometers thick). An ‘aspectratio’ is defined as the ratio of the electrode geometry: electrode 18spacing to thickness, t, of insulator material 20 separating theelectrodes 18 (47:t). The aspect ratio influences clamping pressures.Larger aspect ratios ensure a substantially planar distribution ofelectric field sources. Smaller electrode spacing ensures better contactwith a substrate attached to either side of electroadhesive device 10 e.

Insulating layer 44 is relatively planar, includes opposing surfaces 23and 25, and comprises insulating material 20. In one embodiment,insulating layer 44 is compliant and conforms to forces applied thereto.In a specific embodiment, insulating layer 44 includes a thickness lessthan about 2 millimeters. In another specific embodiment, insulatinglayer 44 includes a thickness less than about 0.1 millimeters. Layer 44may also include a material such as mylar that is bendable but notsubstantially stretchable.

An acrylic elastomer is suitable for use as insulating layer 44. Theacrylic elastomer may be pre-strained to increase its dielectricstrength. Pre-strain of a polymer may be described, in one or moredirections, as the change in dimension in a direction afterpre-straining relative to the dimension in that direction beforepre-straining. The pre-strain may comprise elastic deformation ofpolymer and be formed, for example, by stretching the polymer in tensionand fixing one or more of the edges while stretched. In one embodiment,the pre-strain is elastic. An elastically pre-strained polymer could, inprinciple, be unfixed and return to its original state. The pre-strainmay be imposed at the boundaries using a rigid frame or may also beimplemented locally for a portion of the polymer. In one embodiment,pre-strain is applied uniformly over a portion of the polymer to producean isotropic pre-strained polymer, e.g., 300% by 300% in bothdirections. Pre-strain suitable for use with the present invention isfurther described in U.S. Pat. No. 7,034,432, which is incorporated byreference for all purposes.

In one embodiment to improve clamping forces, electroadhesive device 10e reduces the thickness of insulating layer 44 and/or the pitch 47between electrodes 18 to help the device 10 e better conform to surfaceroughness of a wall surface 12. This brings the opposite polarityelectrodes closer to the substrate material 16 and thus increase thefield effects. In a specific embodiment, device 10 e includes a 16micron thick dielectric material with electrode spacing 47 of about 1millimeter.

The electrodes 18 may also be patterned on the same surface ofinsulating layer 44. FIG. 6B shows an electroadhesive device 10 f inaccordance with another embodiment of the present invention.Electroadhesive device 10 f includes interdigitated electrodes sets 60and 62 on the same surface 23 of a compliant insulating layer 44.

This embodiment decreases the distance between the positive electrodes18 in set 60 and negative electrodes 18 in set 62, and allows theplacement of both sets of electrodes on the same surface ofelectroadhesive device 10 e. Functionally, this eliminates the spacingbetween the electrodes sets 60 and 62 due to insulating layer 44. Italso eliminates the gap between one set of electrodes (previously on thebottom surface 25) and the wall surface 12 when the top surface 23attaches to the wall. Both of these changes increase electroadhesiveforces between electroadhesive device 10 e and the attaching substrate16.

Patterning electrodes 18 at micrometer scales also provide an increasein clamping pressures. Another embodiment for micromachining involvespatterning electrodes into insulated “cilia” hair-like structures, orscales. FIG. 6C shows an electroadhesion device 10 i, a variation of thedevice 10 e, using conducting cilia 55 in accordance with anotherspecific embodiment of the present invention. Cilia 55 include smalldeformable fiber-like structures the increase intimate contact with arough surface 12 (from FIG. 5).

In one embodiment, each electroadhesion cilium 55 has two electrodesembedded in a dielectric insulator such as silicone. The electroadhesioncilia then conform to local surface roughness on wall surface 12, whilethe flexible backing, such as insulating layer 44, to which theelectroadhesion cilia attaches, conforms to global irregularities in awall surface 12. In another specific embodiment, a conducting wire withan insulating coating is coated with another conductive layer. In thiscase, the electroadhesive voltage is applied between the inner coreelectrode and the outer ring through the insulating coating. In theembodiment of FIG. 6C, each cilium 55 has only one electrode and thecilia are simply deformable and compliant hair-like structures connectedto the flat electrodes similar to those in FIG. 6A or 6B. The cilia inthis embodiment may be coated with an insulator (not shown) depending onan anticipated conductivity of a substrate being adhered to. Geometriessuch as these, which can be implemented via micromachining and in somecases using traditional molding or hand assembly techniques depending onthe scale, allow the effective gap between the wall surface 12 andelectrodes in electroadhesion cilia to decrease, both initially anddynamically, as described above, thus enabling large clamping pressuresand electroadhesive forces. Resistance to peeling forces is alsoincreased using cilia because of their large total peel line (each ciliahas a high perimeter length relative to it's cross sectional areacompared to a larger structure).

Increases in clamping pressures provided with patterned electrodes 18may be varied and increased by design. In one embodiment, the size 45and pitch 47 between electrodes 18 in the electroadhesive device isreduced to increase field strength per unit area. In general, theelectroadhesive forces are proportional to the average of the square ofthe field strength. Increasing size and spacing between electrodes 18also decreases weak or dead zones in the field distribution. In anotherembodiment, the insulating material 20 of layer 44 is selected oraltered to minimize internal charge leakage through the electroadhesivedevices. This also decreases the power requirement for clamping. Amaterial may also be added as the adhering surface of the device andselected to increase fiction coefficients, thereby increasing theeffective lateral clamping pressure even for the same normal clampingpressure.

So far, the electroadhesive devices have been described with respect totwo using voltages. More complication electrical provisions arecontemplated. FIG. 4I shows an electroadhesive device 10 i in accordancewith another embodiment of the present invention.

Electroadhesive device 10 i includes a combination of multiple voltagesapplied to the electrodes 18. In this case, three voltages arealternated on the electrodes 18: V1, V2, and V3. For example, V1 may beabout 5 kilovolts, V2 may be about 0 volts, while V3 is about minus (−)5 kilovolts. This creates fractal electric fields 22 due to charges onthe electrodes of varying strengths in the substrate 16, as shown inFIG. 4I. Fractal electric fields refer to electric fields of differentstrengths created by the electrodes and voltages applied thereto. Morethan three voltage levels may be used, along with other spacingarrangements of the electrodes.

Another embodiment to create fractal electric fields 22 of varyingelectric field strengths in the substrate 16 is to apply phase shiftedinput to electrodes 18. In this case, a control circuit applied timevarying voltages 59 a-59 c to the electrodes 18. One suitable example ofphase shifted input for the three voltage pattern of FIG. 4I is shown inFIG. 4J. Other varying voltage patterns are also suitable for use.Changing pitch between the electrodes may also achieve fractal electricfields 22 of varying strengths as shown.

A multi-modal approach to increasing adhesion forces combineselectroadhesion with existing wall-crawling methods. For example, smallangled spikes (that embed into a surface) may be added to anelectroadhesion clamping device 10 to added greater lateral forces thatoppose gravity and allow for forward motion.

A second hybrid adhesion embodiment involves the use of electroadhesionin combination with a suction cup. For example, the suction cup mayinclude an electroadhesive device about the perimeter of a ring for thecup, which increases the ability for the perimeter to maintain intimatecontact with a wall surface, thereby reducing leaks and improves suctionforces. The suction cup may be actuated by any suitable suction cuptechnology, such as pneumatic means, pumps, or electroactive polymeractuation.

Electroadhesive devices 10 may also be modified to increase resistanceto peeling. FIGS. 7A-7C illustrate the concept of peeling for anelectroadhesive device 10. FIGS. 7A and 7C illustrate when peeling maybe encountered, and the resultant peeling moment 80 and force 82 for avertical wall and ceiling, respectively.

As described above, electroadhesive device 10 has strong forcecapability perpendicular and parallel to wall 14, but may be sensitiveto peeling forces and moments that cause rotation and detachment of aportion of the device 10 away from the wall 14, such as the clockwisepeeling moment 80 shown in FIG. 7B. The force required to peel anelectroadhesion device 10 off a substrate depends on the electroadhesiveforces (such as measured by clamping pressure) and on the length of thepeeling line (i.e. the length of the line in the peeling zone thatdefines detached areas from attached areas). The minimum force requiredto peel the electroadhesive device 10 off a substrate is its minimumpeeling force for that substrate as defined here.

In addition to a high minimum peeling force for device 10, it is oftenbeneficial to have a high total peel energy. The total peel energy asdefined here is the mechanical energy required to detach electroadhesiondevice 10 from a substrate. By analogy to the strength of materials,total peel energy may be considered a measure of peel toughness whereasminimum peel force is a measure of peel strength. The total peel energymay often be approximated by the minimum peel force times the distancedevice 10 must be pulled to remove it by peeling. The compliant andelastic features of this invention are particularly useful forincreasing total peel energy. If, for example, the compliance comes fromsoft elastomer layers, flaps, or cilia, and if the peel force is enoughto appreciably stretch these elastic features, then the total peelenergy is increased by the elastic stretching energy. A high total peelenergy is helpful in these instances because it makes the device 10 moreable to resist disturbances such as temporary shocks, jolts, andvibration.

Peeling moment 80 may cause the electroadhesive device 10 to detach,first partially, and then potentially fully from top to bottom. Partialdetachment is shown in FIGS. 7D (top view) and 7E (side view), where 112represents portions of the electroadhesive device 10 surface that arestill attached to wall 14, while 114 represents a portion of wallsurface 12 that has already peeled away. The length of peel line 110 isa measure of the force or torque that can be resisted by theelectroadhesion without peeling.

In one embodiment, an electroadhesive device 10 is adapted to increasepeel-resistance. In a specific embodiment, electroadhesive devices 10increase the cumulative length of the peel line 110, thereby increasingthe peeling force to detach from the wall. For electroadhesive device 10g shown in FIGS. 7F and 7G, this solution is achieved using a gridstructure 116 to subdivide the overall electroadhesive device area 30(which consists of both attached areas 112 and detached areas 114; seeFIG. 7F). Grid structure 116 increases the cumulative length of peellines 110 for electroadhesive device 10 by separating the lines. Whilegrid structure 116 provides a more peel-resistant electroadhesivedevice, the resulting increase in bending stiffness of device 10 mayimpede the ability of the electroadhesive device 10 to maintain intimatecontact with wall surface 12 and thus may reduce clamping forces.Techniques to compensate and increase the clamping force were describedabove.

FIGS. 7H and 7I show a peel-resistant electroadhesive device 10 h inaccordance with another embodiment of the present invention.Electroadhesive device 10 h includes a sealed plenum-like structure 130that creates a relative vacuum pressure in a space 132 that is at leastpartially sealed by the surface of insulating layer 44 opposite to theadhering surface. The vacuum pressure in space 132 limits deformation ofthe compliant insulating layer 44. Although a sealed air chamber isshown in FIGS. 7H and 7I, similar peel resistance may be achieved usinga soft elastomer, gel, or even liquid inside the cavity instead of air.

Functionally, once electroadhesive device 10 h attaches to wall 14,peeling of the electroadhesive device 10 h has to increase the volume ofthe sealed space 132. This decreases pressure in space 132, thus causingthe vacuum pressure space 132 to resist further peeling. This passivestructural modification has demonstrated an increase in peeling force of2.6× and 1.8× for wall and ceiling electroadhesion forces, respectively.

Having discussed several simple electroadhesive devices, electrodes 18and insulating material 20 will now be expanded upon.

Electrodes 18 include a conductive material that communicates electricalenergy. Generally, electrodes suitable for use with the presentinvention may include any conductor, shape and material provided thatthey are able to supply and transmit an electrostatic adhesion voltagethat induces an adhering electric field into a nearby wall or structure.The electrodes may be deposited on a surface of the electroadhesivedevice as a conductive coating, or embedded therein. Conductive coatings18 or layers may include any suitable electrical carrier, such as acarbon impregnated polymers, a metallic spray or sputtered coating, orany other suitable conductor available to one of skill in the art.Electrode 18 may also be made up of an insulated or non-insulatedelectrical wire. Because electrostatic forces typically operate at highvoltage and low current, the conductive material 18 need not be highlyconductive. In fact, the natural conductivity of carbon fibers or othercarbon particles, even diminished by mixing them into a non-conductingpolymer matrix, is more than sufficient in many cases. Embedding theelectrode 18 in insulating material 20 or under another materialprotects the electrodes.

The present invention may employ a wide variety of electrode 18materials. In one embodiment, the electrodes 18 are rigid. Suitablematerials for rigid electrodes 18 may include a metal such as copper,aluminum, gold, brass, and conductive polymers.

In some cases, “rigid” electrode materials may also be considereddeformable if they are sufficiently thin. For example, aluminized mylaror gold-coated polyimide are both typically quite flexible and compliantbecause they can easily bend in thin shapes, though they arenon-extensible (non-stretchable). Very thin metals and other conductorscan also be advantageous because a local electrical breakdown canself-heal by locally vaporizing electrode material until the field canbe supported again. This self-healing process makes the electroadhesiondevice 10 more robust. Related self-healing methods are known, forexample, in the capacitor prior art as a way to make the device morerobust. Another method to construct compliant electrodes out of “rigid”or non-extensible materials is to construct it with in-plane of out ofplane corrugations (such as zigzags) that can be expanded withoutstretching the electrode. In another embodiment, electrodes 18 arecompliant and change shape or extend with device 10. Suitable compliant,extensible electrodes materials include conductive greases such ascarbon greases or silver greases, colloidal suspensions, high aspectratio conductive materials such as carbon fibrils and carbon nanotubes,and mixtures of ionically conductive materials. Other suitable materialsinclude graphite powders, carbon black, colloidal suspensions, silverfilled and carbon filled gels and polymers, and ionically orelectronically stretchable conductive polymers. In a specificembodiment, an electrode suitable for use with the present inventioncomprises gold-coated polyimide or kapton. Aluminized mylar can also beused as a lower cost alternative but is more prone to cracking and“open” circuits, particularly in the connection region. In anotherspecific embodiment, stretchable electrodes can be made by mixing LSR5810 silicone elastomer made by Nusil Technology of Carpenteria, Calif.with conductive carbon black (Vultan(R) XC72R) made by Cabot Corporationof Alpharetta, Ga. in a 5:1 ratio. Solvents such as naptha or hexane canbe used to lower the viscosity of the electrode during mixing ordeposition. Various types of electrodes suitable for use with thepresent invention are known in the prior art of complaint conductors andexamples are described in commonly owned U.S. Pat. No. 7,034,432, whichis incorporated by reference herein in its entirety for all purposes.

Carbon based electrodes may be patterned by spray deposition and screenprinting for example. In a specific embodiment, a compliant electrode 18includes a thin coating applied in a selective area or pattern to asurface of insulating material 20 (FIGS. 6A and 6B). For example, thecompliant electrode may include a carbon-impregnated elastomer patternedwith a stencil. The compliant electrode 18 adds little stiffness to adeformable electroadhesive device 10. In addition, thecarbon-impregnated polymer adds little thickness to electroadhesivedevice 10. In one specific embodiment, the carbon-based electrodes canbe deposited to form strands on the electroadhesive device 10 in theshape of cilia discussed in FIG. 6C. In another embodiment, an electrodecan be patterned by removing material. For example, etching away or evenpeeling away certain areas of aluminum coating on an aluminized mylarsheet can result in a patterned electrode left behind on the mylarsubstrate.

Insulating material 20 includes any material that can separate chargesfrom adjacent electrodes 18, substantially maintain the electrostaticadhesion voltage between the first electrode and the second electrode,or otherwise allows the power supply providing the electrostaticadhesion voltage to maintain the electrostatic adhesion voltage. In oneembodiment, spacing between electrodes 18 determines the conductivitylimit of insulating material 20; if the electrodes 18 are too close,even a good insulator may be weakly conductive at some high voltagesthat may be used in device 10. In some cases, air pockets may act as theeffective insulation between electrodes 18 (see FIG. 4G or 5B forexample).

In one embodiment, insulating material 20 includes a compliant material.In a specific embodiment, insulating material 20 includes an elasticmodulus less than about 10 MPa. In another specific embodiment,insulating material 20 includes an elastic modulus less than about 1MPa.

Insulating material 20 may also include more rigid materials. Some rigidmaterials may be thinly cast, such as mylar; this allows the thinmaterial to be bendable and conformable but not substantiallyelastically extendable. In order to support larger loads, a stifferstronger insulating material 20 may be used.

Specific examples of insulation material 20 may include a compliantrubber or elastomer, acrylic elastomers, mylar, polyimide, silicones,silicone rubbers, payralin, PMDS elastomer, silicone rubber films,polyeurethane, polypropelene, acrylics, nitrile, latex, fiberglass,fiberglass cloth, glass, and ceramic. One suitable insulation material20 is silicone RTV 118 as provided by GE Silicones of Wilton, Conn. PVCfilms (popularly used as cling wrap for food packaging) are alsosuitable for use and have a good balance of elasticity, elastic modulus,and dielectric breakdown strength. Since these materials are made tohave enhanced static electricity, they have low leakage rates and highdielectric breakdown strength. Breakdown tests on PVC films hasindicated a breakdown strength of 250 to 550 V/micrometer, which is wellabove the minimum required for electroadhesion. Another suitablematerial is mylar, due to its excellent breakdown strength and lowinherent leakage (and power consumption).

Electroadhesive device 10 may be packaged in a vast array of formfactors, shapes, and sizes. Padded and flat electroadhesive devices 10have already been illustrated. Electroadhesion tracks, suitable forground-based locomotion, are shown below in FIGS. 10A-10C.Electroadhesive device tires are shown in FIGS. 11A and 11B. The abilityto make the support structure 24 rigid or soft also permits customshapes with varying surface textures. It is also important to note thatelectroadhesive device 10 is substantially scale invariant:electroadhesive device sizes may range from 1 square centimeter toseveral meters in surface area. Larger and smaller surface areas alsopossible, and may be sized to the needs of an application.

Electroadhesive device 10 can adhere to a wide variety of materials 16,structures 14 and surfaces 12. Sample surfaces 12 includes those foundon: indoor and outdoor walls, rocks and trees and other obstacles foundin natural environments, sloping structures such as bridge spans andsides of storage tanks, ceilings, and doors and windows. The indoor andoutdoor walls may include vertical walls, angled walls, ceilings, andthe like. Sample structures 14 include buildings and parts thereof,trees, cars, planes, boats, and other vehicles larger than the device ora robot that uses the device 10, bridges, storage tanks, and pipes.

Electroadhesion as described herein also provides robust attachment to awide variety of wall materials including but not limited to: concrete,wood, glass, plastics, ceramic, granite, rocks, asphalt, and metals. Forexample, the present invention works with most wall materials such asconcrete, wood, steel, glass, and drywall commonly found in everydaybuildings. Non-perfect conditions and surfaces are also suitable forattachment, such as damp surfaces, dusty surfaces, and uneven and/orrough surfaces. Rough surfaces are suitable for use and were describedabove with respect to FIGS. 5A-5C.

Electrical Control and Circuits

The electroadhesive devices typically rely on electrical control andinput. For instance, at the very least, a minimum amount of circuitry isneeded to provide electrostatic adhesion voltages to the electroadhesivedevice 10. FIG. 8 shows control and conditioning circuitry 150 suitablefor providing a suitable electrostatic adhesion voltage to electrodes 18of electroadhesive device 10 in accordance with one embodiment of thepresent invention.

Control circuitry 152 is configured to determine when a suitableelectrostatic adhesion voltage is applied to electrodes 18. Circuitry152 may include a processor or controller that provides on/off signalsthat determine when electrostatic adhesion voltages area applied, andwhat magnitudes. Circuitry 152 may also determine the times associatedwith a charge and discharge cycle on the electroadhesive device 10.

Conditioning circuitry 154 may include any circuitry configured toperform one or more of the following tasks: voltage step-up, which isused when applying a voltage to the electrodes 18, conversion between ACand DC power, voltage smoothing, and recovery of stored electrostaticenergy. Conditioning circuitry 154 may be designed to receive power froma low-voltage battery 156. For example, in robotics applications,conditioning circuitry 154 may receive a voltage from a conventionalbattery, such as those less than 40 volts, and increase the voltage toan electrostatic adhesion voltages above 1 kilovolt. The low voltagepower source such as the battery may be replaced by another electricalsource such as a small photovoltaic panels similar to the ones used inmany handheld calculators. In one embodiment, conditioning circuitry 154includes a transformer configured to provide voltage step-up toelectrostatic adhesion voltages described herein. In a specificembodiment, conditioning circuitry 154 includes a model No. Q50-5 asprovided by EMCO High Voltage Corporation of 70 Forest Products Road,Sutter Creek Calif. Leads 158 extend from conditioning circuitry 154 tocommon electrode 71, which simultaneously communicates with electrodes18 of electroadhesive device 10.

More complex charge control circuits may be developed, depending on theconfiguration of electroadhesive device 10, and are not limited to thedesign in FIG. 8. Also, some of the circuit functions may be integrated.For instance, one integrated circuit may perform the functions of boththe step-up circuitry 154 and the charge control circuitry 152.

The voltages provided to electroadhesive device 10 may vary. In oneembodiment, AC actuation is applied to the electrodes. In some cases,electrostatic forces on a dielectric substrate have been shown to relaxover a time constant under steady DC actuation. This phenomena can alsooccur in insulator 20 if it traps charge. However, by alternating thepolarity of charge on each of the compliant electrodes 18 at a highfrequency, electroadhesive forces can be maintained or even enhanced. Ina specific embodiment, the AC signal includes a frequency above 1 Hz.Other higher and lower frequencies may be used. In another embodiment,multiple sets of electrode 18 are used with applied AC voltages offsetin time or shifted in phase. This allows one set of electrodes 18 tomaintain electroadhesive forces while the AC voltage in another settemporarily passes through 0 voltage difference. In another embodiment,a DC actuation may be provided to the electrodes. In some of the caseswith DC actuation, a moderately low insulator resistance may provide aleakage path to achieve a fast release when voltage is switched off. Inother cases, a fixed amount of charge of opposite polarity to the DCactuation may be pulsed into the electrodes 18 to provide release whendesired. In this case, the fixed amount of charge may come from anexternal capacitor or one that is a part of the conditioning circuitry154 with a capacitance equal to that of the electroadhesive clamp 20.

Switching and response times of electroadhesive device 10 will then varywith the electrical equipment and signal applied to the electrodes 18. A5 Hz signal, with a voltage rise time of one-tenth of the time period,provides a charge and discharge cycle of 20 milliseconds.

In general, electroadhesion requires a small amount of power to adhereto a substrate. The power requirement is small because electroadhesionmay be primarily thought of as a capacitive device. This implies thatwith appropriate selection of insulation material 20 to minimize leakagecurrents (of the order of micro- or nano-amps in most cases), thereactive power remains small. Resistivity of insulator 20 may be reducedif trapped charge becomes a problem as long as the leakage currentremains acceptable.

A quick power modeling of electroadhesion will now be provided to helpassess power requirements in robotics and other applications. This isespecially valuable in understanding the endurance of a robot when in aperch or hold position with no locomotion, where the robot still needsto stay attached to a wall or ceiling for extended periods of time.

As an illustrative example, an electroadhesive area of 15 square inchesmay support the weight of a 1.5 lb robot at an electroadhesion pressureof 0.1 psi (a conservative clamping pressure that accommodates wet andrough surfaces and the possible presence of particulates). This area maybe decreased to 3 square inches for many designs. The electroded areacan be roughly estimated at 50 percent of the overall area of thecontacting surface 80 of device 10 (e.g., 1 millimeter wide electrodeswith 1 millimeter spacing between them). Although the capacitance of theelectroadhesion would depend on the substrate 16 to which the device 10is being clamped, a simplifying estimate can be obtained byapproximating the capacitance through the thickness of insulatingmaterial 20 when the substrate 20 is a conductive material such assteel. This estimate is a conservative one since the effective chargepath for nonconductive substrates is greater and results in a lowercapacitance. The capacitance of a parallel plate capacitor is:

C=εo εA/d  (Equation 2)

where εr is the dielectric constant of the material of interest, εo thepermittivity of free space, A is the electroded area on device 10, and dis the insulated electrical path length between the electrodes 18 (i.e.excluding the distance through the conductive substrate and otherconductors). With an acrylic with a dielectric constant of 4.7 and athickness of approximately 25 microns as insulating material 20,Equation 1 produces a capacitance of 0.8 nF for an area of 3 squareinches (note that d is twice the acrylic thickness in this case). Thepower required to charge and discharge this resistor is given by:

P=½C V2 Fη  (Equation 3)

where V is the voltage to which the capacitance is charged (e.g., 3-4kV), η is the efficiency of the low-to-high voltage conversion, and F isthe frequency of the charging and discharging. For wheeled robots asdescribed below, the charging and discharging occurs as the wheelrotates, e.g., it uses a commutator design as described below. However,when the robot is stationary, the compliant electrodes may be chargedwith bipolar AC voltage in order to prevent buildup of charge in thesubstrate, which for some substrates may gradually decrease the clampingforce. For purposes of illustration, assuming an AC charge/dischargefrequency of 20 Hz and an efficiency of 50 percent, device 10 uses of0.26 W of power.

In some cases, additional power may be required to overcome leakageresistance of the insulator material 20. Because the resistance betweentwo successive electrodes 18 is fairly large (e.g., in the order ofGigaohms), the leakage currents involved are of the order of microampsor even nanoamps. As such, the I2R resistive losses are a small fractionof the power required to charge and discharge the effective capacitancebetween the compliant electrodes.

In a fully operational robot as described in the next section, most ofthe power for mobility is therefore for the drive motors andcommunication equipment, similar to that in a ground vehicle. It mayalso be noted that the above analysis assumes that the charge from eachcycle is dissipated through a resistor or other means. With someadditional circuitry that recovers charge and shuttles it acrosscapacitors, the electronic efficiency may exceed 80 percent, whichdecreases the power required for clamp-on hold and increasing theendurance of the robot in a perch mode. It should also be noted that ifAC charging and discharging is not needed, as is often the case, thenmuch lower power is needed. For example, on many surfaces andelectroadhesion device 10 configurations, DC voltages work well and thedevice 10 may be simply peeled off for removal rather than needing toturn off power. The peeling may be done manually or, on a robot, partsof electroadhesion device may be peeled off while other parts areattached (for example using electroadhesive wheels or treads; see laterdescriptions of robots). In such cases where DC power can be used, thepower consumption can be dramatically reduced and in one embodiment itwas estimated that only 100 microwatts of power would be needed to holda 1 lb. (0.45 kg) robot on a wall.

FIG. 9 shows a method 200 of adhering objects using electroadhesion inaccordance with one embodiment of the present invention.

Method 200 typically begins by positioning an electroadhesion device inproximity to a surface of a substrate (202). As mentioned below withrespect to the robots, this may be automated using mechanical means suchas a wheel or track. A user may also do so manually in the case of thedouble-sided electroadhesive device 600 of FIG. 16A.

Control circuitry in electrical communication with electrodes in theelectroadhesion device then applies a differential electrostaticadhesion voltage to the electrodes (204). In some cases, the steps 202and 204 may be reversed, i.e. the voltage to the electrodes may be firstapplied before positioning the electroadhesion pad near the substrate.The voltage difference may be applied substantially simultaneously, orat different times. Suitable electrostatic adhesion voltages—to createan adhering electric field and electrostatic force between theelectroadhesion device and substrate—were described above.

Insulation material 20 maintains separation of the electrodes andmaintains the voltage differential for electrostatic adhesion (206).This maintains the adhering electric field and electrostatic forcebetween the electroadhesion device and substrate.

The device then adheres to the substrate (208). In anther embodiment,the electrostatic forces are used to increase traction of theelectroadhesive device relative to a surface. Enhanced traction isuseful for mobility (of robots or other devices) on inclines or lowslippery surfaces such as ice for example.

In one embodiment when the electroadhesion device includes a deformablematerial between the electrodes and at the surface of the substrate, thecompliance permits the electrodes to move closer to the surface and thisdynamically increase the electrostatic force and adhesion strength(210). This is shown and explained above with respect to FIGS. 5A-5C.

When it is desirous to cease the electrostatic adhesion—to move theelectroadhesion device relative to the wall for example—the controlcircuitry then removes differential electrostatic adhesion voltage(212). If the electroadhesion device is to be moved to another location,method 200 may repeat as desired. In other cases, the electroadhesivevoltage may be always on and the robot moved by mechanically peelingaway the electroadhesive device from the surface without turning thevoltage off.

Devices and Applications

Electrically controlled adhesion finds wide use in a wide variety ofdevices and applications. For example, many devices designed or adaptedfor wall crawling are well suited to use electroadhesive devices andmethods described herein. Some examples described in further detailbelow include wall crawling robots, electroadhesion equipment worn by aperson for wall crawling, and electroadhesion ladders that allow thetopside or the entire length of a ladder to adhere to a wall so that aperson may climb the ladder. Many other devices may use theelectroadhesive devices and methods as described herein.

Many devices in this section, such as the robots, permit robustperformance. They are able to: clamp and unclamp with electroadhesionspeeds of response less than 1 second, conform around and clamp to roughsurfaces, operate in dusty or damp environments, transition acrossorthogonal surfaces on walls, etc. In addition, the electroadhesivedevices add little weight; many standalone pads may weigh less than anounce.

Numerous robot illustrative designs will now be discussed. In oneembodiment, electroadhesion is used to enable a wall-crawling robot.This may include adding electroadhesive devices to rotary locomotiverobots, such as those using wheels or tracks (FIGS. 10-12).

FIG. 10A shows a wall-crawling robot 350 a in accordance with a specificembodiment of the present invention. Robot 350 a includes two tracks 352on left and right sides of a chassis 354. In some cases, a singlecontinuous elecroadhesive device may be employed that attaches to bothleft and right side of chassis 354 (similar to a conveyor belt).

Chassis 354 provides structural support between wheels 354, whichinterface with track or tracks 352. Chassis also includes all portablelocomotion requirements for robot 350, such as a battery or other powersource, one or more motors to turn wheels 354, wireless communicationequipment and interfaces, payload such as a camera, etc.

Tracks 352 include one or more compliant electroadhesive devices ontheir outer surface. In one embodiment, the electroadhesive devicescontinuously follow along the track length without interruption. Boththe mechanical structure of tracks 352 and compliant electroadhesivedevices disposed thereon can conform around rough or uneven surfaces.Tracks 352 offer a large electroadhesive surface area, without requiringan appreciable mass. In addition, the tracks offer a reliable, robust,and proven way for locomotion on unstructured and unpredictableterrain—both flat and vertical.

To turn, one or both tracks 352 slide relative to a surface. Duringturning, electroadhesion between one or both tracks 352 and the surfacemay be reduced. In addition, control of the electroadhesion pressures onindividual tracks 352 can be used to steer the vehicle without anyadditional mechanisms, thereby providing a simple and lightweightsteering mechanism. In other cases, the speed of track 352 may bechanged on one side of the robot relative to the other.

FIG. 10B shows a wall-crawling robot 350 b in accordance with anotherspecific embodiment of the present invention. Robot 350 b includesmultiple segments 372 and 374 and a hinge 376 that permits pivotingbetween segments 372 and 374. As will be described below, thisfacilitates transitioning between horizontal surfaces (floors andceilings) and vertical surfaces (walls). FIG. 10C shows wall-crawlingrobot 350 b traversing from a horizontal surface 380 to a vertical wall382 and to another horizontal surface 384.

Referring to FIG. 10B, segments 372 and 374 are each capable of pivotingrelative to the other, about hinge 376, while each capable ofindependently maintaining adhesion to a wall surface. This allowswall-crawling robot 350 to successfully negotiate the inner and outercorners of a building, for example. Although not shown, robot 350 mayinclude more than two segments, such as three, four, ten, or more.

Hinge 376 attaches to segments 372 and 374 and permits rotational motionbetween segments 372 and 374. Hinge 376 may be passive or articulated.An articulated hinge 376 uses an actuator to controllably rotate thehinge and move one segment relative to the other. For example, theactuator may include a lead screw-motor device, or a motor with agearbox, in order to provide torque. The articulation may actuate for 90degrees, or greater, of rotation in either direction in order tonegotiate orthogonal surfaces. A passive hinge 376 reacts to the forcesapplied to it by segments 372 and 374.

As shown in FIG. 10C, for an inner corner 381 (e.g., floor 380 to avertical wall 382), the forward (upper) segment 374 raises and foldsupwards while the trailing (lower) segment 372 provides traction andelectroadhesion until the top segment 374 clamps to the vertical surface12. Although not shown, wall-crawling robots 350 may be capable ofmovement in both forward and reverse directions (e.g., by reversing thedirection of wheels). In this case, segment 372 becomes the forwardsegment while segment 374 becomes the trailing segment 372.

For an outer corner 385 (where vertical wall 382 meets top surface, orroof, 384), the forward segment 374 first comes into contact with roof384, which is about orthogonal to vertical wall 382, and then drags therest of the robot 350 with it. Once transition of one-half of robot 350has been achieved, adhesion of trailing segment 372 can be switched off,temporarily making the robot 350 a front-wheel drive vehicle until therear tracks gain adhesion to the roof 384 surface. This results in theability to easily transition across orthogonal surfaces and reducespower consumption.

In one specific embodiment, some of the wheels 354 are passive and donot provide rotational power. In another specific embodiment, some ofthe wheels 354 are spring loaded and can move slightly to maintain andincrease the amount of contact with the wall as the robot turns upwards.

As mentioned above with respect to FIGS. 7A-7I, electroadhesive devicesmay be adapted to resist peeling. Peeling also concerns a robot when therobot exerts torques on its electroadhesive devices because its centerof gravity is distant from a wall surface.

One technique to reduce peeling torques for a robot is to make the robotas thin and flat as possible. Robot 350 also exerts a clamping forcenormal to wall 14 so that the robot does not peel off the wall. As asimplified example, a low-profile robot weighing 5 N (about 0.5 kg or 1lb mass) might have a center of mass located 0.075 m (about 3 inches)from the wall surface 12. In this case, the peeling torque exerted is 5N×0.075 m, or about 0.375 N-m (about 3 in-lbs). For a 0.25 m (10 inch)long robot that pivots at the bottom and has an electroadhesive clampingforce distributed roughly uniformly along its length so that the averagemoment arm is roughly 0.125 m (5 inch) from the bottom, the normalclamping force needed is about 0.375 N-m/0.125 m=3 N. Assuming a modestclamping pressure of 1.5 kPa (about 0.2 psi), the required 3 N clampingforce can be achieved with an electroadhesive device of 3 N/(1500Pa)=0.002 m2 or about 3.1 square inches in size for most electroadhesionmaterials on a variety of wall surfaces. In general, rougher surfaceswill require greater clamping pressures or larger electroadhesive deviceto make the robot even more robust.

Another technique to reduce peeling uses a double tracked robot 350 b asshown in FIG. 10B. Robot 350 b includes two tracked segments: a frontsegment 374 and a rear segment 372. In one embodiment, the front segment374 is smaller than the passive rear segment 372 and pushed forward bythe rear segment. In this case, rear segment 372 includes the motors andgearing to move robot 350 b.

For a robot climbing up a vertical wall (see FIG. 10C), the peelingmoment due to the center of gravity offset typically tries to rotate therobot about its lowermost point. The front segment 374 provides a forceand moment that counteracts this peeling moment on the rear segment 372.Ribs, or rigid cross members, may also be added onto the track 354 ofeither segment to effectively segment the electroadhesive devices alongthe track 354 and interrupt full peeling. A mechanical extension or“tail” can also be added to many robots using electroadhesion. The tailforces the rotation point lower, thus increasing the effectiveness ofelectroadhesion to resist peeling torque by increasing the moment arm.

FIG. 11 illustrates a wall-crawling robot 400 using electroadhesion in aflattened tire configuration in accordance with another specificembodiment of the present invention. For sake of brevity, only thefeatures of robot 400 not included in device 350 will now be described.Thus, components such as the chassis 372 and batteries are not detailed.

Robot 400 includes compliant and elastic electroadhesive devices 10disposed on the outer surface, and around the circumference, of fourunder-inflated tires 402. Each tire 402 resembles a deflated tire inorder to increase contact area between the electroadhesive device 10disposed thereon and a surface to be adhered to.

Each tire 402 includes two sets of compliant electrodes 404: compliantelectrodes 404 in an inner electrode set 406, and compliant electrodes404 in an outer electrode set 408. The electrode sets 406 and 408 eachinclude finger electrodes 404 that extend substantially across the tire402 width, and are circumferentially offset from each other.

In one embodiment, an insulating and compliant layer (comprising acompliant material and not shown in FIG. 11A) separates the electrodesets 406 and 408. In a specific embodiment, the insulating layerincludes an insulating elastomer layer. The electrode sets 406 and 408are disposed on opposite sides of the insulating layer to preventelectrical breakdown across a gap between the electrodes 406 and 408. Inanother embodiment, the electrodes 406 and 408 may be located on thesame side of a compliant substrate. This side may be either on theinside of a thin insulating layer, or on the outside of such a layer indirect contact with the substrate.

Both electrode sets 406 and 408 are also embedded in tire 402 under anouter layer (again, transparent and not shown in FIG. 11A so theelectrodes can be seen, although the actual outer layer need not betransparent). The inter-electrode insulating layer and outer layer areusually thin so that the electrodes 406 and 408 remain close to the tiresurface.

In operation, the flattened tires 402 increase the amount of surfacearea contact between the electrodes and a surface 12. As described abovewith respect to the method of FIGS. 5A-5C, the compliance of tire 402and electroadhesive device 10 disposed thereon also permits dynamicincreases in the surface area contact to provide greater surface areaattachment and higher adhesion forces. In some cases, it may not benecessary to flatten the tire if the electroadhesive force from aninflated tire is sufficient to support wall climbing. In such cases, thepower required to drive the robot forward may be lower than in the caseof using a flattened tire.

Electrically, activation of compliant electrodes 404 near the substratesurface may use bipolar AC voltages to achieve both robust clamping andfast declamping (so as to not retard the motion of the vehicle). The ACvoltages are also useful when the robot is stationary in order to avoiddeterioration of clamping force over time because of trapped charge inthe substrate or insulator. Deactivation of the electrodes permits theremoval of dust, moisture, or other substances that may adhere to thewheel 402 (or track) during normal operation and reduce adhesiveefficiency. Thus, by switching off the electroadhesion away from theclamping surface, dust particles no longer actively adhere to the wheels402 (or tracks 354 of robot 350), and as described in further detailbelow, permit a simple passive cleaning device such as a brush 432 toremove any additional debris on the wheel or track. In some cases DCvoltages are satisfactory in maintaining adequate electroadhesive forcesas noted earlier. Brushes may still be helpful in DC operation bysweeping the electroadhesive surfaces that adhere to the substrateclean. In the DC mode the dust and debris may accumulate at the brushlocation until it can fall off away from the critical surfaces.

In an AC mode, in order to achieve transfer of charge to and from thecompliant electrodes at select times in the tire 402 rotation, anelectrical commutator may be used. The commutator is configured to applycharge to the electrodes 404 during a bottom angle of the rotating wheel402 when the tire is in contact with surface 12 (or just before), andremoves this charge from a top or side angle of rotation that is not incontact with the substrate to aid cleaning. The commutator thus allowsselective rotational electroadhesion and activation of theelectroadhesive devices by regulating when electrical energy supplied tothe electrode sets 406 and 408. The commutator is relatively simple andpermits the application of bipolar AC signals to the appropriateportions of wheel rotation, and removal of charge from other portions ofthe wheel rotation without requiring numerous signals. Many commutatorssuitable for use herein are commercially available from a wide varietyof vendors. The commutator may send high voltage on or off theelectroadhesive device directly if it has suitable high voltagecapability. Alternately, a commutator can send low voltage power tosmall voltage converters inside the tire, or to high voltage switchessuch as solid state high voltage switches on the tire that switch asingle source of high voltage to the correct electrodes. Alternativelyto a commutator, a slip ring or other mechanism for selective rotationalelectrical actuation may be used, possibly in conjunction with increasedinsulation or lower number of effective channels to accommodate highvoltages. One slip ring suitable for use is a model AC 246 from MoogCorporation of Blacksburg, Va. Note that the commutator or othermechanism for controlled rotational electrical provision may be used inother robots described herein (i.e., with tracks or flapped tires) withonly minor modifications.

Other techniques to provide power to the electrodes are suitable foruse. Alternatively, without brushes, a voltage bus may be fixed relativeto the body 372 of robot 400 to contact spokes 418 at desired rotationallocations to actuate the electroadhesive devices at desired angles. Inanother specific embodiment, a robot may use a high-voltage slip-ring,with four to eight channels, to provide signals to the rotatingelectroadhesive surfaces. Each sector of the wheel or track connects toone channel of the slip ring and activate when that sector is close tothe substrate surface. In this case, a trigger sensor—that determinesthe position of each sector relative to the wall or ground—may be usedto command input voltages.

Robot 400 permits easy steering. Indeed, off-the-shelf robots withmodified wheels (to add flattened tires 402 and a commutator, forexample) can be used for robot 400. Further, with independent axles 436for each wheel, minimal sliding is necessary in order to achieveturning, allowing the application of full electroadhesive clamping forceat all times, if desired. Alterations to robot 400 are contemplated.Other suitable configurations involve similar electroadhesive devices 10integrated into rigid wheels of a robot.

Robot 400 also includes an optional cleaning system configured to cleanelectroadhesive devices 10 and surfaces of tires 402. The cleaningsystem may remove moisture, dust and other foreign particles that mayrest between the pads and a wall surface. The cleaning system may beadded to the other robots described herein. For example, cleaning systemmay be added to robot 350 to remove particulates and moisture fromtracks 352.

The cleaning system components may vary with the objects removed fromthe adhesive pads. For example, the cleaning system may include a brush432 (see FIG. 11B or 10A) that contacts the electroadhesive devices ontires 402 as they rotate to a position where they usually do not contacta wall. The brush 432 removes particulates very well. Alternatively, thecleaning system may include a foam material that removes both dustparticulates and moisture from the electroadhesive devices of tires 402or tracks 352 at one of their respective non-adherence positions. Othersubstances that may be removed include oils, dirt, grass, and otherdebris.

In one embodiment, the cleaning system is disposed on a path of movingelectroadhesive devices 10 that does not interfere with where the pads10 clamp to a wall for that robot. Robot 400 uses a side position (notbottom or top) along the rotational path of the tires 402 and permitsthe electroadhesive devices 10 to interface with the brush 432, whichprovides a simple and passive cleaning system that continuously cleanssurfaces of each tire 402. Typically, the adhesion is turned off (e.g.,using the commutator) when the wheel or track comes in contact with thecleaning pad, allowing for debris and liquids to be removed. Since thepressure that needs to be applied to clean a non-adhesive device issmall, the cleaning system adds little added power to achieve sustainedcleaning of the pads.

FIG. 12 shows a wall crawling robot 450 in accordance with anotherspecific embodiment of the present invention. Robot 450 includesflexible electroadhesive devices 452 that extend radially outward fromwheels 454.

Each electroadhesive device 452 is relatively planar, and includes afirst end that attaches to wheel 454 and a second free end.Structurally, each device 452 resembles a flap. As each wheel 454rotates, the electroadhesive devices 452 on each wheel rotate about thewheel axis and eventually: a) comes into contact with a surface ofsubstrate 16, and b) flatten beneath the wheel 454. In both positions,electroadhesive device 452 provides an adherence force to substrate 16.Cumulatively, multiple electroadhesive devices 452 contacting thesurface of substrate 16 provide a force sufficient to hold robot 450aloft on vertical walls, angled walls, ceilings, and the like. In oneembodiment, electroadhesive devices 452 each include a flexible materialas the insulating material 20, such as rubber, which allows the deviceto readily deform.

Flap electroadhesive devices 452 may also be added to tracks 352 ofrobot 350 described above. In this case, one end of a bendable but notsubstantially extendable flap 452 attaches to the track 352 while theother is free to deform relative to the attached end. As each track 352rotates, the flap electroadhesive devices 452 on each track eventually:a) come into contact with a surface of substrate 16, and b) flattenbeneath the track 352 while the flap remains on the bottom side of thetrack attached to the wall. This design increases the amount of timethat flap electroadhesive devices 452 contacts the wall, and increaseselectroadhesive contact area between robot and wall. In addition, flaps452 incorporate increased peel resistance, since the load to support anddrive the robot is applied to the bottom of each flap and issubstantially in a direction that is in the plane of the flaps. Theflaps 452 may also use the increased contact time, while under thetrack, to dynamically increase contact as described in FIGS. 5B and 5C.Such robots have been built, can scale vertical walls of many materials,and reach speeds of about 1 foot per second.

As shown, robot 450 also includes a hinge 376 and two segments attachedthereto. Another embodiment of robot 450 includes a single segment,similar to the chassis of FIG. 10A or 11A. Turning robot 450 usesreduced sliding of pads 452, similar to the flattened tire design ofFIG. 11A. In other cases, two side-by-side units with an articulatedhinge between them can be used to achieve turning without the need toslide relative to the surfaces. Although not shown, hinge 376 andmultiple segments 372 and 374 may also work with the wheeled designs ofFIGS. 11A and 12.

The robots described above are able to robustly climb a variety ofexternal surfaces including rough, dusty, and sometimes dampenvironments, move on interior surfaces, transition between orthogonaland other angled surfaces while maintaining adhesion to at least onesurface, and remain motionless for substantial periods of time on avertical wall or ceiling (also known as ‘perching’). Prior to theelectroadhesive-based robots described above, robots capable of allthese functions did not exist despite having been investigated for manyyears, which hints at the breakthrough by controllable electroadhesionfor wall crawling.

The robots described herein are well suited for a variety of tasks, andmay carry payloads according to those tasks. For example, the robots maycarry a camera for surveillance in dangerous or remote areas. Otherpayloads may be carried. Communications equipment, such ascommunications equipment to relay images captured by the camera and/orcommunications equipment to permit remote control, are also useful andmay be carted by the robot. Such reconnaissance robots are useful fortraversing complex and unstructured terrain, such as random buildings,especially in urban environments for a variety of scouting and othermilitary or police missions.

There is a need in police and fire departments, the military, andindustry for a portable robot device that can be sent into aninaccessible and/or hostile environment. The robots described herein areable to do so and traverse in three dimensions on the ground, walls, andceilings on commonly encountered building substrates, readilytransitioning across the surfaces when necessary. The ability to perchfor long periods of time (more than 60 hours) on a wall or ceiling ornavigate continuously for 3 hours in three dimensions without requiringbattery charging is also useful in many of these applications. Theability to carry a communications link, which permits a user interfaceto control the robot, also extends usage in hostile environments.

Recent military operations in the Middle East and elsewhere havedemonstrated the need for effective tools in urban combat operations.One such tool is a robot that has three-dimensional mobility. Byaffording access in a vertical direction in an urban environment, such arobot can enhance limited communications range at ground level bydeploying communication antennae at much higher levels. Alternately, arobot may carry a surveillance camera and enter a building through adoor, window, or hole in the building and scale the interior walls orceilings of a room—before military personnel enter blindly. Thesesmaller wall-climbing robots can also be deployed by soldiers into anurban combat zone inside a building by releasing them on the ground andsteering them in. These robots may then scale walls surreptitiously andprovide visual cues to the soldier from internal vantage points.

Another common feature permissible in the robots described above issymmetry along three axes (forward and back, left and right as well astop and bottom). The symmetry allows a robot to work from anyposition—regardless of orientation. The upside down symmetry allows therobot to detach from a ceiling and land on a floor, e.g., for rapidrepositioning when necessary. In such situations, in addition to havinggood shock tolerance, the robot is then able to operate in whateverorientation in which it lands so that no power or time is wasted ontrying to change its orientation. In addition, having cameras both foreand aft allows a teleo-operator to see what is going on beneath aclimbing robot, or optimize its perching position for maximum clampingcapability and field of view.

The robots are also surprisingly fast. Many of the wall-crawling robotembodiments described above may operate with speeds of about 0.2 toabout 1 foot per second—while climbing a wall. Faster and slower speedsare also permissible. Since the electroadhesion can be switched off whenthe robot is moving horizontally on the ground or another level surface,the electroadhesive devices would not add any additional friction to therobot under normal operation (where electroadhesion is not needed forlocomotion) and affect ground speeds significantly.

In one embodiment, many of the robots described above and suitable foruse herein are attained with slight modifications to commerciallyavailable robots, or using parts from commercially available robotickits. For example, tracked robot 400 may include a tracked vehiclemodified from a Tamiya Tracked Vehicle Chassis Kit Skill Level I modelno. 3081246 as provided by Edmunds Scientific of Tonawanda, N.Y.Commercially available robotic components, most of which are alreadydesigned for lightweight robots, suitable for use may include motors,speed controllers, battery packs, solar panels, micro receivers or othertransmitters, and/or camera units with transmitters. One suitable motorincludes a Copal 60:1 gear motor model no. 0-copal60 as provided by TheRobot Marketplace of Bradenton, Fla. This motor already comes with aninbuilt 60:1 gear train ratio. One suitable speed controller includes anAnt 150 Dual 5A high speed controller as provided by The RobotMarketplace (part number LB-ANT150-2). One suitable battery includes anApogee 2480 mAh LiPoly rechargeable battery as provided by RC Hobbiesand More of Winsted Conn.

The weight of a wall-crawling robot is important because clamping areasand power consumption to climb a vertical or other wall viaelectroadhesion increases with robot weight. Fortunately, many of theparts listed above are intended for portable robotics and alreadyreasonably light; the electroadhesion parts also add little weight.

The electroadhesion also adds minimal power requirements to the portablerobot, which must usually rely on batteries or some other form ofportable energy. For example, the Copal motor operates at 6 V and arated current of 400 milliAmps. Integrating four such motors in order toindependently drive the wheels of a robot described above provides amaximum power consumption of 9.6 W. Intermittent power may also be usedto actuate an articulated hinge 376, if included. As discussed in thepreceding section on power requirements for electroadhesion, the powerdraw for the wall climbing (around 0.3 W in some instances) representsonly a small increase in total vehicle power

The minimal addition to power draw also results in a small decrease inoverall endurance. Endurance for a robot will depend on its powerconsumption, weight and power supply, among other factors. Manycommercially available lightweight robots weigh less than 1 kilogram andhave typical sizes of about 10 in×10 in and wheel diameters of about 4to 5 inches or track dimensions of about 8 in×2 in. Their endurance willdepend on the battery pack energy capacity that comes with the kit,which may provide an endurance of over two hours in many instances, andcan be increased with added battery capacity. One robot that has beenmodified with electroadhesion tracks in a Tamiya Tracked Vehicle ChassisKit Skill Level I model no. 3081246 as provided by Edmunds Scientific ofTonawanda, N.Y. Modifying these robots with oversized lightweightelectroadhesive wheels or tracks enables mobile robots with little cost.

In other instances, the robots are custom built to fully leverage theadvantages of electroadhesion. In a specific embodiment, a robot bodyincludes a lightweight carbon fiber that provides a highstrength-to-weight ratio.

Other robotic designs are contemplated and permissible. FIG. 13 shows arobot 500 in accordance with another embodiment of the presentinvention. Robot 500 uses flat electroadhesive devices 502 (the pads areshown similar to the grid electroadhesive design of FIG. 7F), eachconnected to a motorized wheel or tread using a 4-bar linkage 504. Inone embodiment shown in FIG. 13, when the wheel rotates, the pads 502move away from the robot but remain in an approximately constantorientation parallel to the wall. In another embodiment, the rotation ofthe wheel can produce a combination of an out of plane motion (to movethe pads away from the wall) as well as in plane motion (to advance thepads while it is away from the wall). In some of these cases involvingmechanically moving the pads away from the wall, it may not be necessaryto switch off the electroadhesion during the robot motion. Using eitherof these embodiments, the power for electroadhesive device 502 can belocated on the device itself, and does not require transfer of chargebetween a rotating frame and fixed frame. The switching of theelectroadhesion can be synchronized to the rotation of the wheel thussimplifying the electronics requirements. More complex robots witharticulated arms having multiple degrees of freedom may also includeelectroadhesive devices 502 distally attached to their distal end.

In a specific embodiment, a robot with electroadhesive devices ‘walks’.These robots have electroadhesive devices that provide controlled on/offclamping and traction when the device touches a wall surface. In anotherspecific embodiment, pads 502 are ‘always on’. In this configuration,the electroadhesive devices 502 provide a normal force between the robotand the wall at all times. Robot 500 includes motors that overcome thefriction from the adhesion of pads 502 and either drag the pads alongthe wall (e.g., a vertical wall) or peels them off as the robot moves.This scheme is simple and allows the clamps to operate continuously.

A walking robot using electroadhesive to assist locomotion may use acommercially available walking robot with minor modifications. This mayinclude adding electroadhesive devices to the legs of a crawling robot,and providing a means of sequencing the electroadhesive actuation incoordination with the leg motions. Examples of such commerciallyavailable robots include robots made to climb walls using suction cupssuch as in the Climb@tron series of robots as provided by EdmundsScientific of Tonawanda, N.Y. In many such cases, a direct replacementof the suction cups with electroadhesive pads can result in more robustwall climbing across a wider variety of substrates. Althoughoff-the-shelf crawling vehicles are generally slow, the ease with whichelectroadhesive devices can be added makes them attractive. A powersupply and control electronics for the electroadhesive devices may alsobe added onboard the robot, but as mentioned above, the electroadhesivedevices consume significantly less power than locomotion for the robot,and the control electronics can also be negligibly small and light.

Other robots and robotic design may employ one or more electroadhesivedevices as described herein. One alternative to wheeled or trackedlocomotion is an inchworm-type robot. This robot uses a separateactuator to move electroadhesive devices relative to each other along awall; the electroadhesive devices take turns clamping to permit theother end of the inchworm-type robot to move. Wall-climbing robotsinvolving such actuators are known in the art, without electroadhesivedevices that is.

Electroadhesion also enables other devices. FIG. 14 showselectroadhesive handwear 550 and electroadhesive leg-pads 552 inaccordance with a specific application embodiment. Handwear 550 includesan electroadhesive device 554 and an interface 556 that attaches toelectroadhesive device 554 and detachably couples to a hand or wrist ofa person. Similarly, leg-pads 552 include an electroadhesive device 558and an interface 556 that attaches to electroadhesive device 554 anddetachably couples about a person's knee as shown.

Electroadhesive handwear 550 and leg-pads 552 allow the person to climbwall 560.

The size of electroadhesive devices 554 will vary with the adherencepressures provided by the electroadhesive devices 554. A conservativeacceptable area may be 100 square inches of electroadhesive devices 554using 4 pads (two handwear pads 550 and two leg pads 552). Assuming 3psi clamping (sliding resistance) pressure, each 25 square inch pad(e.g. 5 inch×5 inch pads) would provide 75 lbs sliding resistance, sothe pads could support up to 300 lbs. More or less electroadhesive areafor handwear 550 and leg-pads 552 may be used.

While interface 556 includes a strap for both handwear 550 and leg-pads552, other pad/person interfaces may be configured to detachably couplean electroadhesive device to a portion of a person. For example,handwear 550 may include a glove, mitten, etc., while leg-pads 552 mayinclude shoes, boots or other leg or foot wear configured to detachablycouple to a portion of a person's leg. In some cases, theelectroadhesive electrodes may be patterned directly onto or worn as acovering over the fabric or clothing of the person.

Electroadhesion permits other devices and methods for a person to climba wall. The methods may be described as 1) placing an electroadhesivedevice on a wall above a person, 2) adhering the electroadhesive deviceto the wall, and 3) ascending the wall using the coupling between theelectroadhesive device and wall. Two examples of this method are shownin FIGS. 15A and 15B.

FIG. 15A shows an electroadhesive scaling device 570 in accordance witha specific application embodiment. Device 570 includes a line 572 andelectroadhesive device 575. An air pressure gun, or other projectiondevice, propels electroadhesive device 575 up wall 576 and places device575 on the wall above the person 577. Electroadhesive device 575 mayinclude its own power supply, contact sensor and switch that initiateselectroadhesion when device 575 hits the wall. Alternately theelectronics are located with the person and line 572 includes suitableelectrical connections to electroadhesive device 575. Electroadhesivedevice 575 may also include a compliant surface to dynamically improveadherence, as discussed above. In some cases, device 575 may alsoinclude mechanical grapplers, hooks etc. to provide additional adherenceto the wall. After device 575 adheres to the wall, person 577 may thenscale the wall using the coupling between the electroadhesive device 575and wall. Line 572 may include rope, twine, or any other suitablelightweight cable.

FIG. 15B shows an electroadhesive scaling device 580 in accordance withanother specific application embodiment. In this case, device 590includes a robot 350 and ladder 592 (or other line 572) attached to atrailing portion of robot 350. Person 577 places the electroadhesivedevices on robot 350 on wall 576 by controlling movement of the robot350. At a desired position, the robot stops and adheres to its currentposition, while the person 577 ascends ladder 592. In some cases, it isdesirable to adhere ladder 592 along its length to the wall 576 toprevent large ladder motions. In such cases, the ladder 592 may beequipped with electroadhesion as well. With resting stops for the personalong the wall or building, this process may be repeated as desired toscale large or high structures.

Another device enabled by electroadhesive devices described hereinincludes robotic grippers. The grippers have one or more electroadhesivedevices that are well suited to grasp and pick up objects. Thesegrippers find use in robotics such as manufacturing and industrialgrippers where fragile items are to be handled without much force.Compliance or actuation in the gripper also permits the electroadhesivedevice(s) to globally shape to an object before electroadhesion isapplied. The grippers are also well suited for picking up dust (anelectroadhesive dust collector), leaves (and electroadhesive leafremover), non-lethal insect traps (for experiments, for example) etc.

In another embodiment, an electroadhesive device is used in a devicethat is configured to provide controllable adhesion of one or moreobjects to a wall or other large structure. FIGS. 16A-16C show adetachable double-sided electroadhesive device 600 in accordance withanother specific embodiment of the present invention.

Device 600 includes electrodes 602 and 604 disposed on opposite sides ofan insulating material 606, as shown in FIG. 16B. More specifically,insulating material 606 includes a relatively flat profile and twoopposing surfaces 603 and 601. Insulating material 606 may be rigid orflexible; in the latter case, device 600 assumes the stiffness of morerigid objects that it adheres to. One or more protective layers 615 maybe disposed over the electrodes. Layers 615 are thin and may include aninsulation material as described above such as mylar.

Electroadhesive device 600 is configured to controllably adhere tomultiple objects simultaneously. This may include one or more objects oneach surface 601 and 603. Together, adhering an object to each oppositesurface 601 and 603 permits two separate objects to be temporarilycoupled together using electroadhesion and device 600. FIG. 16A shows acutaway of device 600 adhering to a wall 610 and adhering to pictureframe 612. In other words, device mechanically couples frame 612 to wall610, and may be used to hang frame 612 on the wall 610.

Device 600 may be thought of as a form of non-permanent adhesion thatdoes not leave an aftereffect of the mechanical connection, in contrastto a hole left by a nail, for the objects it mechanically couplestogether. Post-it Notes and two-sided tape are examples of non-permanentadhesion, but obviously rely on chemical adhesives and are thereforesusceptible to dust, particularly after repeated use. They may alsorequire undesirable tradeoffs between the need to support a significantload and the need to be able to remove them without damage to the wall(for example pulling double-sided tape off a wall may also removepaint). Electroadhesion on the other hand can support larger structuresand objects. Indeed, electroadhesive device 600 may be scaled in sizefrom several square centimeters in surface area to several meters.

Sample objects that may be adhered to include: picture frames,calenders, staplers, cell phones, keys, posters, cords, decorations,banners, car dashboards, flat screen televisions and monitors, radios,lightweight shelves, wallpaper, and lights, for example. Wall 610 mayalternatively include cabinets, the side of a desk, a home appliance,cars, billboards, etc. Electroadhesive device 600 allows a person toutilize typically untapped surfaces and spaces in an office or home, ina non-permanent and non-damaging manner.

While FIG. 16A shows device 600 adhering to one object on each side,device 600 may also adhere more than one object per side. For example,device 600 may be enlarged to resemble a cork-board on which objects areadhered using electroadhesion to the device 600, which itself adheres toa wall.

Switch 608 on side bar 611 is configured to allow a person to turnelectroadhesive device on/off. Contact sensors are suitable for use,along with conventional mechanical switches. Embedded in control bar 611is a battery or other power source such as solar panels and controlcircuitry, such as step-up voltage circuitry, as described above topower electroadhesive device 600. In many cases, the battery can beeliminated by use of a renewable source such as a small photovoltaicpanel. The small amounts of power required can be generated from a solarpanel operating indoors, similar to a solar cell calculator.

In another embodiment, device 600 is one-sided and has a permanent formof attachment on a surface opposite to the adhering surface. This maythen be used to electrostatically adhere multiple objects to device 600,similar to a corkboard.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and equivalents thatfall within the scope of this invention which have been omitted forbrevity's sake. By way of example, although the present invention hasbeen described in terms of several polymer materials and geometries, thepresent invention is not limited to these materials and geometries. Itis therefore intended that the scope of the invention should bedetermined with reference to the appended claims.

1. A robot, comprising: a body; a mechanism for locomotion mechanically coupled to the body; and at least one electroadhesive device mechanically coupled to the mechanism for locomotion and configured to detachably adhere to a foreign substrate, said electroadhesive device including first and second electrodes configured to apply an electrostatic adhesion voltage that produces an electrostatic force between the at least one electroadhesive device and the foreign substrate, wherein said electrostatic force is suitable to maintain a current position of the at least one electroadhesive device relative to the substrate.
 2. The robot of claim 1, wherein the substrate is included in a vertical wall or a ceiling.
 3. The robot of claim 1, wherein the mechanism for locomotion is configured to position the at least one electroadhesive device onto a surface of the substrate.
 4. The robot of claim 1, wherein the electroadhesive device further includes a deformable surface adapted to interface with a surface of the substrate.
 5. The robot of claim 1, wherein the mechanism for locomotion includes tracks or a wheel.
 6. The robot of claim 1, wherein the electrodes include one or more cilium configured to deform to a surface of the substrate when the electrostatic adhesion voltage is applied.
 7. The robot of claim 1, wherein the surface of the substrate is damp or dusty.
 8. The robot of claim 1, wherein the electrostatic force between the device and the substrate is suitable to maintain a current position of the device relative to the substrate despite the presence of a particulate disposed between a surface of the device and a surface of the substrate.
 9. The robot of claim 1, further comprising circuitry configured to provide the electrostatic adhesion voltage between the first electrode and the second electrode, and wherein the circuitry includes step-up voltage circuitry that is configured to receive a voltage from a voltage source, which is less than about 40 volts, and configured to increase the voltage from the voltage source to the electrostatic adhesion voltage, which is above about 500 volts.
 10. The robot of claim 1, wherein the first electrode and the second electrode are less than about 1 millimeter from a surface of the substrate when the electrostatic adhesion voltage is applied.
 11. An electroadhesive device configured to adhere objects together, the electroadhesive device comprising: a body with a first surface and a second surface; a first electrode configured to apply a first voltage at a first location of the first surface; a second electrode configured to apply a second voltage at a second location of the first surface; and a mechanism for locomotion mechanically coupled to the body and at least one of said first and second electrodes, wherein the difference in voltage between the first voltage and second voltage includes an electrostatic adhesion voltage that produces a first electrostatic force between the electroadhesive device and a first object that is suitable to adhere a surface of the first object to the first surface.
 12. The electroadhesive device of claim 11, wherein the body includes an insulation material disposed between the first electrode and the second electrode and configured to substantially maintain the electrostatic adhesion voltage difference between the first electrode and the second electrode.
 13. The electroadhesive device of claim 11, further comprising circuitry configured to provide the electrostatic adhesion voltage between the first electrode and the second electrode, wherein the circuitry includes step-up voltage circuitry that is configured to receive a voltage from a voltage source, which is less than about 40 volts, and configured to increase the voltage from the voltage source to the electrostatic adhesion voltage, which is above about 500 volt.
 14. A method of ascending a wall, comprising: positioning a first electroadhesion device at a first position in proximity to a surface of the wall; applying a first electrostatic adhesion voltage difference between first and second electrodes located on the first electroadhesion device; adhering the first electroadhesion device to the wall surface using a first electrostatic attraction force provided by the first electrostatic adhesion voltage difference; positioning a second electroadhesion device at a second position in proximity to the wall surface; applying a second electrostatic adhesion voltage difference between third and fourth electrodes located on the second electroadhesion device; adhering the second electroadhesion device to the wall surface using a second electrostatic attraction force provided by the second electrostatic adhesion voltage difference; and ascending the wall while one of said first and second electroadhesion devices adheres to the wall.
 15. The method of claim 14, wherein said step of ascending the wall comprises: removing the first electrostatic adhesion voltage on said first electroadhesion device; moving said first electroadhesion device up the wall while said first electrostatic adhesion voltage is removed; repositioning said first electroadhesion device at a third position in proximity to the wall surface while said first electrostatic adhesion voltage is removed; and reapplying said first electrostatic adhesion voltage difference between first and second electrodes located on the first electroadhesion device while said first electroadhesion device is located at said third position.
 16. The method of claim 14, wherein the wall surface has a roughness greater than about 1 millimeter.
 17. The method of claim 14, wherein the wall surface is one of damp, greasy, or dusty. 